The invention relates generally to a brushless cooling fan. More particularly, the invention relates to a high efficiency brushless motor cooling fan for an automotive application.
Internal combustion engines, automotive engines as a prime example, require cooling. Typical cooling systems involve pumping a coolant over the heat generating systems and pumping the heated fluid to a fan-cooled radiator to release the heat to the atmosphere. Typically, a cooling system uses a brushed direct current (DC) motor to power the system fan. However, brushed DC motors are inefficient and prone to mechanical failure. Brushless direct current (BLDC) motors overcome the lower efficiency, susceptibility to mechanical wear and consequent need for servicing, the characteristic limitations of brushed DC motors.
In a BLDC motor, an electronic controller replaces the brush and commutator assembly of the brushed DC motor, which continually switches the phase to the windings to keep the motor turning. BLDC motors have greater reliability, reduced noise, longer lifetime, more power, eliminate ionizing sparks from the commutator, and reduce electromagnetic interference (EMI), allowing for easier compliance with electromagnetic compatibility (EMC) requirements. Since most modern vehicles incorporate computer controls in engine management and other general vehicle operations, reducing EMI is important for the reliability of the overall vehicle.
Brushless motors are more desirable than a conventional brushed motor, but come at the cost of potentially less rugged and more complex and expensive control electronics. These control electronics are not well suited for functioning under the hood of an automobile, where high temperatures generated by the engine create a hostile environment for the complex and expensive electronics. The operating life of the electronics at high temperature is significantly reduced due to higher resistance levels. This limits the reliability of an electronic control system, and consequently, the BLDC motor in high temperature environments. The higher cost, increased complexity and limited reliability at high temperatures have curtailed the adaptation of BLDC components in under-the-hood automotive applications. Modern automobiles with more powerful engines paradoxically need both an efficient, powerful, and reliable cooling system and generate relatively high temperatures hostile to BLDC electronic control systems. Under the hood, automotive components can reach temperatures greater than 100° C., the boiling point of water. The fan assembly is mounted in close proximity to the heat exchanger or radiator, where temperatures approach 110° C. To increase efficiency and operating life, sufficient cooling of the fan motor and its electronic components is imperative.
Many have proposed various answers to improving the cooling system with a brushless motor. Kershaw et al. (U.S. Pat. No. 6,208,052) discloses a heat sink structure at the base of the motor with the shaft of the motor attaching to the heat sink. A control unit circuit board is between the heat sink and a hub in the shroud base. Kershaw et al. (U.S. Pat. No. 5,944,497) previously had proposed an opening in hub where the motor is cooled by air directed by a plate from the high pressure region of the fan to the low pressure region of the fan.
Sunaga et al. (U.S. Pat. No. 6,661,134) proposes a heat sink with supporting legs that are in contact with the electric circuit board so that the heat sink is positioned on the electric circuit board. The radiating fins of the heat sink are exposed to the outside through an opening in the circuit protection case adjacent to the motor. Takeuchi et al. (U.S. Pat. No. 5,947,189) suggests a radiation fin unit of the control device inside the shroud that projects into an air guiding duct on the top of the controller. Nelson et al. (U.S. Pat. No. 6,600,249) proposes the controller of a brushless motor connecting to engine control mechanism and mounted to the side of the fan shroud in housing without any cooling mechanism.
In addition to the heat generated by the internal combustion engine, a BLDC motor generates heat internally. Although brushless motors typically operate cooler than conventional brushed motors due to the elimination of commutator-brush friction, common to both BLDC and conventional motors is the presence of copper magnet-wire coils found on the stator or armature. When electrical current passes through these coils, the electrical resistance within the copper magnet-wire produces heat. High temperatures increase electrical resistance, requiring more electricity to generate the same magnetic field and producing even more heat, creating the potential for thermal runaway, leading to burnout of the coils and destruction of the motor and other critical components.
Many have suggested ways to cool a fan motor itself. Hong et al. (U.S. Pat. No. 7,244,110) proposed a fan with a specially designed hub, the inside of the hub having vanes that become a radial-flow blower drawing cooling air through a brushed motor, not a BLDC motor. Yapp et al. (U.S. Pat. No. 5,489,186) proposes stationary flow control vanes that attach to the housing, moving and recirculating the airflow in a pathway between the fan and the housing. Hayashibara (U.S. Pat. No. 4,428,719) discloses a rotor of a BLDC motor fixed to a centrifugal fan while a stator is fixed to the scroll concentrically with the rotor, cooling the motor and eliminating the necessity for the motor housing. De Filippis (U.S. Pat. No. 5,217,353) suggests a BLDC motor having a casing with holes for taking in air from outside for ventilating the interior of the brushless motor and a rotary part with holes which act as outlet ducts for the internal ventilation air.
The marketplace demands that these axial fans that are used in automotive cooling systems be both efficient and compact to fit in the limited space under the hood. Many have proposed way to either increase the air flow or condense the space required for the fan assembly. Alizadeh (U.S. Pat. No. 5,755,557) suggests a hub portion with a set of blades extending to a circular support and a second set of blades extending radially outwardly from the support. Similarly, Jorgensen (U.S. Pat. No. 4,962,734) discloses a fan ring around the fan blades and an assembly around the ring bearing the weight of the fan. Longhouse et al. (U.S. Pat. No. 4,685,513) incorporates an enveloping shroud which is fixed to the radiator and which has integral bracket structure for supporting the fan motor centrally therein. Carlson et al. (U.S. Patent Application Publication 2006/0257251) also has a hub with radially extending fan blades to an annular shroud, and a second set of fan blades extending from the shroud. Zeng (U.S. Pat. No. 5,591,008) discloses a motor fastened to a shroud, and a fan fastened to the motor.
Besides the necessity of cooling the motor and the controller for efficient operation of the fan, the blades of the fan impeller must be balanced to reduce unwanted vibration in the rotating fan assembly. The ends of the impeller blades typically attach to a rotating rim which must be annularly balanced for smooth rotation without vibrating. Similarly, many have thought about balancing wheels or crankshafts on automobiles where wobble is undesirable. Turoczi (U.S. Pat. No. 3,663,328) discloses indicia cemented to a side wall of a tire for balancing. Benjamen (U.S. Pat. No. 5,591,008) describes adding plugs to a wheel to balance a tire as well as pockets on a vibration damper around the crankshaft. Warner (U.S. Pat. No. 2,454,852) discloses a fan on a rotary valve of the crankshaft having balancing holes drilled in rim. Darnell (U.S. Pat. No. 2,558,737) suggest balance weights added onto the surface of the rim of the fan, which would create turbulent air flow. Wrobel (U.S. Pat. No. 5,591,008) discloses a fan impeller with one or more guide rings provided with pockets or bores for weights.
A special challenge for an automobile owner who desires to switch to a BLDC fan as part of customizing the vehicle is finding a universal BLDC fan that will work in his or her vehicle. It is desirable to produce a BLDC that adapts to many different makes and models of cars by accepting a range of voltage inputs to the controller and can adjust the fan speed based on engine requirements. Mackelvie (U.S. Pat. No. 7,121,368) proposes to control the fan speed with some type of speed sensor and a potentiometer on the flap on an axle. Samuel et al. (U.S. Pat. No. 4,124,001) discloses a temperature sensing system to vary fan speed with a potentiometer. Makarana (U.S. Pat. No. 7,088,062) suggests a method using a pair of fans, the second fan controlled by a variable frequency pulse width modulated (PWM) control signal to meet cooling requirements of an engine. Wilke (U.S. Pat. No. 4,347,468) proposes an electronic variable speed automotive blower control system controlled by a potentiometer on the dashboard. Lazebnik et al. (U.S. Patent Application Publication 2010/0119389) suggests a modular brushless motor that may be reconfigured for different applications and power levels by varying the number blades on the fan and coils in the stator.
While these units may be suitable for the particular purpose employed, or for general use, they would not be as suitable for the purposes of the present invention as disclosed hereafter.